The present invention generally relates to various aspects related to brown pigments containing iron and chromium. In particular, the present invention relates to brown pigments having desirable weathering characteristics, methods of making the brown pigments, plastics and other materials containing the brown pigments, and methods of using the brown pigments.
Iron oxide is often used with other components to make brown Complex Inorganic Color Pigments (CICP). A CICP is a pigment made by heating a number of different metal oxides. Relatively large, coarse, and/or hard particles often lead to problems in some CICP applications.
The large, coarse, and/or hard CICP particles may be employed in substances such as concrete. However, CICP particles used for coloring coatings, plastics, lacquers and synthetic resins are typically subjected to intensive grinding. The disadvantages associated with intensive grinding include the undesirable formation dust, difficulties in measuring the ground CICP particles, and difficulties in dispensing with the ground CICP particles.
Moreover, in order for CICP particles used for coloring coatings, plastics, lacquers and synthetic resins, high temperature stability is often required since these materials are often processed or exposed to high temperatures. Coatings, plastics, lacquers and synthetic resins also typically require pigments with good weathering characteristics since lengthy exposure to the outdoor environment is common. In the case of vinyl siding for homes, outdoor exposure lasts many years. Many brown pigments unfortunately lack good weathering characteristics.
The ability to tint pigments is also a desirable characteristic. A pigment with high tinting strength has broader applications and may be used in a number of different settings. Unfortunately, many brown pigments lack strong tinting characteristics.
Some brown CICP formulations have one or two desirable properties as well as several undesirable properties. For example, some brown pigments are strong, but have poor weathering characteristics, poor heat resistance, weak tinting strength, undesirable color shades, and/or costly starting materials. Specifically, conventional PBr 29 is strongly brown but has poor weathering characteristics. It is therefore not commonly employed in outdoor applications where such characteristics are required. Conventional PY 164 (based on manganese-antimony-titanium), often employed as a brown pigment, has good weathering characteristics, but poor tinting strength.
Given these circumstances, when employing a brown CICP formulation, one must accept a compromise on at least one desirable property. There is thus an unmet need in the art for a brown CICP formulation having many desirable properties including good weathering.
The present invention provides brown CICP formulations that possess high pigment strength, excellent weathering characteristics, high temperature resistance, and excellent tinting strength. The brown CICP formulations of the present invention possess many desirable characteristics thus minimizing the compromises typically required when selecting a brown pigment.
One aspect of the invention relates to a brown pigment composition with excellent weathering resistance containing iron oxide, chromium oxide, and one or more alumina and/or silica components. Another aspect of the invention relates to a method of making a brown pigment involving combining iron oxide, chromium oxide, and one or more alumina and/or silica components to form a mixture and heating the mixture to provide brown pigment particles. Yet another aspect of the invention relates to a plastic composition containing a major amount of a plastic material and a minor amount of a brown pigment composition containing iron oxide, chromium oxide, and one or more alumina and/or silica components.
The present invention provides brown iron-chromium pigments that possess at least one of high pigment strength, good weathering characteristics, high tinting strength, high temperature resistance, small particle size, stable during handling, stable to oxidation, and highly dispersible.
The brown iron-chromium pigments contain at least three components; namely, iron oxide, chromium oxide, and one or more alumina and/or silica components. The brown iron-chromium pigments optionally contain other components such as a binder, dispersant, and/or mineralizer. The iron oxide and chrome oxide form a crystal structure typically represented by the formula [Fe,Cr]2O3, corresponding to a PBr 29 pigment, wherein the crystal structure contains more iron than chromium.
The iron oxide of the brown iron-chromium pigments contributes to the strength of the pigment. Iron oxide primarily contains yellow iron oxide; that is, Fe2O3.H2O or FeOOH (hydrated iron (III) oxide). Forms of yellow iron oxide include xcex1-FeOOH and xcex3-FeOOH. Other forms of iron oxide, which may be used in addition to yellow iron oxide include Fe3O4 (iron (II, III) oxide) also known as FeO.Fe2O3, Fe2O3 (iron (III) oxide including xcex1-Fe2O3 and/or xcex3-Fe2O3), Fe(OH)2, and Fe(OH)3. Iron oxides are commercially available and/or may be made from iron oxide precursors.
Although not necessary, it is preferred to employ iron oxide or iron oxide precursors having a relatively small particle size. For example, iron oxide having an average particle size (by weight) of about 5 xcexcm or less is employed. In another embodiment, iron oxide having an average particle size (by weight) of about 1 xcexcm or less is employed.
In one embodiment, the brown iron-chromium pigments of the present invention contain from about 30% to about 80% by weight of iron oxide. In another embodiment, the brown iron-chromium pigment contains from about 35% to about 75% by weight of iron oxide. In yet another embodiment, the brown iron-chromium pigment contains from about 40% to about 70% by weight of iron oxide.
The chromium oxide of the brown iron-chromium pigments contributes to the strength of the pigment. Chromium oxide primarily contains Cr2O3 (chromium (III) oxide), but may also contain chromium (VI) oxide. In one embodiment, the brown iron-chromium pigments do not contain chromium (VI) oxide, or contain less than about 0.001% by weight chromium (VI) oxide. Chromium oxide is commercially available and/or may be made from chromium oxide precursors. Chromium oxide precursors include chromium acetate, chromium bromide, chromium chloride, chromium fluoride, chromium nitrate, and chromium sulfate.
Although not necessary, it is preferred to employ chromium oxide or chromium oxide precursors having a relatively small particle size. For example, chromium oxide having an average particle size (by weight) of about 5 xcexcm or less is employed. In another embodiment, chromium oxide having an average particle size (by weight) of about 2 xcexcm or less is employed.
In one embodiment, the brown iron-chromium pigments of the present invention contain from about 5% to about 50% by weight of chrome oxide. In another embodiment, the brown iron-chromium pigment contains from about 10% to about 45% by weight of chromium oxide. In yet another embodiment, the brown iron-chromium pigment contains from about 15% to about 40% by weight of chromium oxide.
In some instances, the ratio of iron to chromium in the resultant pigment falls within a suitable range for maximizing color strength and/or maintaining crystal structure indicative of a PBr 29 pigment. This crystal structure is represented by the formula [Fe,Cr]2O3. This structure is determined/confirmed using X-ray diffraction. In this connection, in one embodiment, the ratio of iron to chromium is from about 1:1 to about 5:1 by weight (which also corresponds to the amounts of iron oxide and chromium oxide initially combined). In another embodiment, the ratio of iron to chromium is from about 1.5:1 to about 4:1 by weight. In yet another embodiment, the ratio of iron to chromium is from about 2:1 to about 3.5:1 by weight. In most embodiments, there is more iron in the brown iron-chromium pigments than chromium.
The PBr 29 type pigment of the present invention has a crystal structure that is different from the crystal structure of PBr 35 pigments, which have a spinel structure. PBr 35 pigments have a structure represented by the formula FeCr2O4 or FeO.Cr2O3. Spinel structures have the general formula AB2O4. The PBr 29 type pigment of the present invention does not have a spinel structure. The PBr 29 type pigment of the present invention has a crystal structure that is different from the crystal structure of PG 17 pigments, which have a hematite structure. PG 17 pigments have a structure represented by the formula Cr2O3. The PBr 29 type pigment of the present invention does not have a hematite structure.
The one or more alumina and/or silica components of the brown iron-chromium pigments contribute to the weathering and heat resistance properties. The alumina and/or silica component contains at least one alumina component and at least one silica component or the alumina and/or silica component contains at least one alumina-silica component. Alumina components contain at least aluminum and oxygen atoms and include alumina (aluminum oxide, Al2O3), aluminum hydroxide (Al(OH)3) or alumina trihydrate (Al2O3.3H2O). Silica components contain at least silicon and oxygen atoms and include silicates and silica (silicon dioxide) such as powdered silica, fused silica, amorphous silica, arc silica, fumed silica, fused silica. Silica may be derived from sand, quartz, flint, and diatomite. Alumina-silica components contain at least aluminum, silicon, and oxygen atoms and include alumina-silica fiber (made from molten alumina and silica), aluminosilicates, attapulgite, bentonite, halloysite, illite, kaolin, and montmorillonite.
Kaolin includes hydrous kaolin, calcined kaolin, and meta-kaolin. In this connection, heat treated alumina-silica components may be employed, such as calcined attapulgite, calcined bentonite, calcined halloysite, calcined illite, and calcined montmorillonite.
In one embodiment where the alumina and/or silica component contains at least one alumina component and at least one silica component, the alumina and/or silica component contains from about 40% to about 70% by weight of at least one alumina component and from about 30% to about 60% by weight of at least one silica component. In another embodiment where the alumina and/or silica component contains at least one alumina component and at least one silica component, the alumina and/or silica component contains from about 45% to about 65% by weight of at least one alumina component and from about 35% to about 55% by weight of at least one silica component.
Even though one or more alumina and/or silica components are incorporated into the brown iron-chromium pigments of the present invention, a spinel structure and/or a hematite structure are not obtained.
Although not necessary, it is preferred to employ one or more alumina and/or silica components having a relatively small particle size. In one embodiment, kaolin having an average particle size (by weight) of about 5 xcexcm or less is employed. In another embodiment, kaolin having an average particle size (by weight) of about 2 xcexcm or less is employed.
In one embodiment, the brown iron-chromium pigments of the present invention contain from about 2.5% to about 50% by weight of one or more alumina and/or silica components. In another embodiment, the brown iron-chromium pigment contains from about 5% to about 45% by weight of one or more alumina and/or silica components. In yet another embodiment, the brown iron-chromium pigment contains from about 7.5% to about 40% by weight of one or more alumina and/or silica components.
The optional mineralizer of the brown iron-chromium pigments may contribute to the strength of the pigment, induce minor color changes in the pigment, and/or reduce the heating temperature required to make the pigment. Mineralizers include metal fluorides, metal chlorides, and metal sulfates. Specific examples of mineralizers include BaF2, SrF2, CaF2, MgF2, NaF, KCl, KF, NH4Cl, BaCl2, SrCl2, CaCl2, MgCl2, NaCl, BaSO4, SrSO4, CaSO4, Na2SO4, and MgSO4, MoO3, and the like. These compounds are commercially available and/or may be made using methods known in the art.
In one embodiment, the brown iron-chromium pigments of the present invention optionally contain from about 0.01% to about 10% by weight of a mineralizer. In another embodiment, the brown iron-chromium pigment optionally contains from about 0.1% to about 5% by weight of a mineralizer. In yet another embodiment, the brown iron-chromium pigment optionally contains from about 0.5% to about 2% by weight of a mineralizer. In still yet another embodiment, the brown iron-chromium pigment consists essentially of iron oxide, chrome oxide, one or more alumina and/or silica components and optionally a mineralizer such as barium fluoride.
In some instances, the ratio of iron oxide to mineralizer such as barium fluoride falls within a suitable range for maximizing color strength. In this connection, in one embodiment, the ratio of iron oxide to the mineralizer is from about 10:1 to about 70:1 by weight. In another embodiment, the ratio of iron oxide to the mineralizer is from about 30:1 to about 50:1 by weight.
The brown iron-chromium pigments of the present invention may further optionally contain at least one inorganic material. Such inorganic materials include titanium dioxide, boron oxide, and salts such as sodium chloride or other alkali metal salts. When present, these supplemental inorganic materials are present from about 0.01% to about 10% by weight.
In one embodiment, the brown iron-chromium pigments of the present invention do not contain cobalt. In another embodiment, the brown iron-chromium pigments of the present invention do not contain nickel. In yet another embodiment, the brown iron-chromium pigment consists essentially of iron oxide, chromium oxide, and kaolin. In still yet another embodiment, the brown iron-chromium pigment consists essentially of iron oxide, chromium oxide, and aluminum hydroxide and/or silica. In another embodiment, the brown iron-chromium pigment consists essentially of iron oxide, chromium oxide, and alumina and/or silica.
In one embodiment, the brown iron-chromium pigments of the present invention further contain at least one of a binder and a dispersant. In such embodiments, the binder and/or dispersant are present in an amount from about 0.01% to about 2% by weight. In another embodiment, the brown iron-chromium pigments of the present invention do not contain a binder and/or a dispersant (a dispersant-free pigment, a binder-free pigment, or a dispersant/binder-free pigment).
Generally speaking, the brown iron-chromium pigments of the present invention are made by combining the three required components and one or more optional ingredients to form a mixture, heating the mixture, and reducing the particle size of the resultant powder, if necessary and/or desired, for a given end use.
Optionally, after combining at least the iron oxide, chromium oxide, one or more alumina and/or silica components, and one or more optional ingredients to form a mixture and before heating, the mixture is blended. Blending or mixing is conducted by any suitable means including using a blender, using a Waring mixer, and the like. Blending promotes the formation of a uniform mixture. Blending also promotes the formation of a uniform mixture after heating.
The mixture of components is then heated to form a solid solution in the form of a powder. In a preferred embodiment, the mixture of components is heated to a calcination temperature to form the solid solution of a powder. The atmosphere during heating is typically air, but an oxygen rich (containing more than about 21% by weight oxygen) atmosphere, or an inert gas atmosphere may also be employed. Inert gases include nitrogen, helium, neon, argon, and xenon.
During heating, the brown pigment is initially formed and substantially all of the oxide precursors, if present, are converted to their corresponding oxides. The Loss-on-Ignition (LOI) is a measure of the relative amount of a substance which is converted to its corresponding oxide during calcination. The LOI of the CICP formulations according to the present invention are typically from about 1% to about 20% by weight. In another embodiment, the LOI of the CICP formulations according to the present invention are typically from about 2% to about 15% by weight.
Heating is performed using any suitable apparatus known in the art such as a rotary kiln, tunnel kiln, Harrop kiln, shuttle kiln, Pereny kiln, rotary calciner, vertical calciner, high temperature cyclone, and the like. The temperature for heating is generally from about 650xc2x0 C. to about 1,300xc2x0 C. In another embodiment, the calcination temperature is from about 675xc2x0 C. to about 1,100xc2x0 C. In yet another embodiment, the calcination temperature is from about 700xc2x0 C. to about 1,000xc2x0 C. The mixture is heated for a sufficient period of time at the calcination temperature to form a solid solution. In one embodiment, the mixture is heated from about 1 to about 5 hours at the calcination temperature. In another embodiment, the formulation is heated from about 2 to about 4 hours at the calcination temperature.
In one embodiment, the mixture is placed in a suitable heating apparatus that is at the calcination temperature. In another embodiment, the mixture is placed in a suitable heating apparatus and the temperature is increased (ramped) to the calcination temperature. In this embodiment, the temperature is increased to the calcination temperature over a period of time from about 1 to about 12 hours.
The resultant CICP composition, which is typically in powdered form, may be optionally processed to reduce particle sizes or particle size ranges to more useful sizes or more useful size ranges. Any suitable apparatus normally used for the mechanical agitation of solid materials may be utilized including blenders, pulverizers, grinders, mixers, rotating cylinders, tumbling barrels, ball mills, hammer mills, jet mills, roller mills, disc mills, and the like. In many instances, application of shear mixing or jet milling is sufficient to disperse and/or reduce particle sizes. In other instances, pulverizing the heat treated composition is sufficient to disperse and/or reduce particle sizes.
The resultant brown CICP composition contains particles having a relatively small particle size; that is, having an average size (by volume) from about 0.01 microns to about 10 microns. In another embodiment, the brown CICP composition contains particles having an average size from about 0.1 microns to about 5 microns. In yet another embodiment, the brown CICP composition contains particles having an average size from about 0.25 microns to about 2 microns.
In one embodiment, resultant brown CICP composition contains particles having a substantially spherical shape of the particles, flow characteristics are markedly improved compared to conventional brown pigment compositions. As a result of the substantially spherical shape of the particles, the particles tend not to agglomerate or aggregate. Decreased agglomeration and/or aggregation leads to reduced residue levels. Consequently, use of the brown CICP composition in paints, coatings, inks, plastics and the like may be facilitated.
The resultant brown iron-chromium pigments of the present invention have a relatively high absorption capacity for visible light for a brown pigment. This is confirmed by the lightness/darkness value, commonly represented by L*. The lightness/darkness value is determined by combining 1.5 g of the pigment with 10 g of titanium dioxide, and incorporating the combination into 100 g of rigid polyvinyl chloride to form a plaque, and testing the plaque. On one hand, many commercially available brown pigments have L* values in the upper 60""s, such as from 66 to 70, which is often too light to effectively perform as a brown pigment in some applications. In one embodiment, the brown iron-chromium pigments of the present invention have L* values of about 65 or less. In another embodiment, the brown iron-chromium pigments have L* values of about 63 or less. In yet another embodiment, the brown iron-chromium pigments have L* values of about 62 or less.
In one embodiment, the brown iron-chromium pigments of the present invention have L* values of about 57 or more. In another embodiment, the brown iron-chromium pigments have L* values of about 58 or more. In yet another embodiment, the brown iron-chromium pigments have L* values of about 59 or more.
The resultant brown iron-chromium pigments of the present invention have a brown shade. Brown shade is commonly measured by b* values, wherein a positive value indicates a yellow tinge and a negative value indicates a blue tinge. The resultant brown iron-chromium pigments of the present invention also have a red shade. Red shade is commonly measured by a* values, wherein a positive value indicates a red tinge and a negative value indicates a green tinge. The shade is determined by combining 1.5 g of the pigment with 10 g of titanium dioxide, and incorporating the combination into 100 g of rigid polyvinyl chloride to form a plaque, and testing the plaque. In one embodiment, the brown iron-chromium pigments of the present invention have a* values of about 6 or more and b* values of about 3 or more. In another embodiment, the brown iron-chromium pigments have a* values of about 7 or more and b* values of about 5 or more. In yet another embodiment, the brown iron-chromium pigments have a* values of about 10 or more and b* values of about 8 or more.
The brown CICP compositions according to the present invention have high tinting strength. Tinting strength is the ability to be lightened, while retaining original color, with a white pigment such as titanium dioxide.
The brown CICP compositions according to the present invention can be incorporated into any material requiring color. Examples of materials in which the brown CICP compositions may be incorporated include paints, coatings, inks, tapes, plastics, fibers, ceramics, concrete, mortars, and the like. Specific examples of inks include printing inks and lacquers, and specific examples of plastics include thermoplastic and thermosetting materials, natural resins and synthetic resins, polystyrene and its mixed polymers, polyolefins, in particular polyethylene and polypropylene, polyacrylic compounds, polyvinyl compounds, for example polyvinyl chloride, polyvinyl fluoride, polyvinyl acetal, polyvinyl alcohol, and polyvinyl acetate, polyesters and rubber, and also filaments made of viscose and cellulose ethers, cellulose esters, polyamides, polycarbonates, polyurethanes, polyesters, for example polyglycol terephthalates, and polyacrylonitrile.
Typically, a minor amount of the brown CICP compositions may be incorporated into a major amount of a paint, coating, ink, tape, plastic, fiber, ceramic, concrete, mortar, and the like. Major amounts include at least 50% by weight whereas minor amounts include less than 50% by weight.
See, for example, with regard to ink: R. H. Leach, editor, The Printing Ink Manual, Fourth Edition, Van Nostrand Reinhold (International) Co. Ltd., London (1988), particularly pages 282-591; with regard to paints: C. H. Hare, Protective Coatings, Technology Publishing Co., Pittsburgh (1994), particularly pages 63-288; and with regard to plastics: T. G. Webber, Coloring of Plastics, John Wiley and Sons, New York (1979), particularly pages 79-204. The foregoing references are hereby incorporated by reference herein for their teachings of ink, paint and plastic compositions, formulations and vehicles in which the brown CICP compositions of this invention may be used including amounts of colorants.
Especially when incorporated in film or fiber forming materials, such as paints, coatings, and plastics, the brown CICP compositions according to the present invention display strong and bright brown color while not degrading the integrity and uniformity of the resultant films, fibers, and plastics. The brown CICP compositions not degrading the integrity and uniformity of the resultant films, fibers and plastics which can be as thin as about 3 mils, and even about 2 mils.
When incorporated into plastics, especially polyvinyl compounds and polyolefins, the brown CICP compositions according to the present invention not only display strong and bright brown color, but also exhibit excellent weathering characteristics. As a result, plastics containing the brown CICP compositions may be advantageously employed in outdoor uses or other harsh environments.
The following examples illustrate the present invention. Unless otherwise indicated in the following examples and elsewhere in the specification and claims, all parts and percentages are by weight, all temperatures are in degrees Centigrade, and pressure is at or near atmospheric pressure.